Low density webs are used to produce absorbent tissue products (e.g. facial tissues, bath tissues and other similar products) are designed to include several important properties. For example, it is desirable that the products have good bulk, a soft feel and absorbency. It is also desired that the product have good strength and resist tearing, even while wet. Unfortunately, it is very difficult to produce a high strength tissue product that is also soft and highly absorbent. Usually, when steps are taken to increase one property of the product, other characteristics of the product are adversely affected.
For instance, softness is typically increased by decreasing or reducing cellulosic fiber bonding within the tissue product. Inhibiting or reducing fiber bonding, however, adversely affects the strength of the tissue web.
Softness may be enhanced by the topical addition of a softening agent to the tissue web. In the prior art, a polymer (e.g. polyolefin) is suspended in a liquid (e.g. water) to form micro-dispersion beads. When this dispersion is applied to a Yankee dryer during a creping process, the dispersion liquid is evaporated and the remaining polymer dispersion beads melt to form a film. The molten film is then transferred onto the web (e.g. tissue) and creped off the Yankee surface to become a non-continuous polymer film on the surface of the tissue. Referring to FIGS. 1A-D, the polymer film on the creped tissue does not retain any morphological structure of its micro-dispersion beads. Although the dispersion applied by creping makes the low density webs feel softer, creping is not always an option. For a tissue machine without creping, the dispersion can be only applied onto the tissue either before drying when it is still wet or after drying in a post treatment stage. Unfortunately, if the dispersion is applied to a low density web in these two situations, it tends to penetrate the web, reduce mass efficiency, and form hydrogen bonds between pulp fibers. Hydrogen bonding creates a very stiff product that is not soft to the touch.
As such, there is a need for a method for applying a composition to a non-creped web so that the web remains soft to the touch. There is an additional need to apply a composition to a substrate that either maintains or improves the substrate tensile strength.